1. Field of the Invention
This invention relates in general to certain new and useful improvements in circuit arrangements for providing multiple output voltages from a single input voltage, with only a single power transformer, as well as a circuit arrangement which uses trailing edge modulation for providing amplitude modulation and, again, only with a single power transformer. The circuit more preferably provides the amplitude modulation with resonant synchronous rectification using this single power transformer. Specifically, the converter circuit is used in combination with the amplitude modulation circuit arrangement to provide a single DC to DC converter circuit.
2. Brief Description of Related Art
New requirements mandating minimum operating efficiencies are now requiring AC to DC power supplies to deliver usable voltages to modern computer systems under various load conditions, while maintaining minimum efficiencies of greater than eighty percent. While power supplies capable of performing this feat have been available for some time, the costs of multiple power supplies in mainstream applications have caused some difficulty in their utilization.
Previous power supplies utilized for this high efficiency application have, many times, been resonant in nature. However, these prior art power supplies have required multiple power transformers to deliver the necessary voltages to the downstream loads. This multiple transformer approach, while effective at solving some of the technical issues associated with multiple output resonant power supplies, add significant cost to the design, as well as impacting the density due to the additional power transformer requirements. Additionally, prior art approaches to multiple output resonant power supplies have suffered from high line frequency ripple components in the DC outputs, due to the lack of gain in the prior art techniques.
Prior art resonant converters overcome the widespread loading and cross-loading and the changing resonating inductance issue by utilizing two power transformers, one for the 12 volt output and one for the 5 Volt and 3.3 Volt outputs. Since the 5 Volt and 3.3 Volt outputs are very close to each other in magnitude, it is possible to live with the different reflected leakage inductance without too much difficulty. The 12 Volt power transformer however, is a separate transformer with a separate resonant tank to accomplish a balanced resonant network for both of the transformers.
This new approach solves this need for multiple transformers and the resultant dilemma which is created. The invention, in one major aspect utilizes a new technique called trailing edge modulation. This trailing edge modulation approach, coupled with another major aspect of the invention namely, a new amplitude modulation scheme, allows the use of resonance with synchronous rectification coupled with one single power transformer. This allows for a lower cost approach than conventional low efficiency power supplies which are utilized today.